1. Field of the Invention
The invention relates to thermo pump-cooled generators that exhaust heated air from the rotor end windings, which are constrained within a generator retaining ring, into the rotor/stator annular air gap. More particularly the invention relates to rotor windings for thermo pump-cooled generators that have an internally formed cooling passage, with a cooling inlet on a radial underside of the rotor end winding portion and a cooling outlet on a radial upper side of the winding axial portion that is oriented within the generator air gap.
2. Description of the Prior Art
Known generators have a generator rotor with rotor windings, including axial portions that are positioned within generator rotor channels and end portions with turn bends. Electrical generator retaining rings at each axial end of the rotor circumscribe and support the rotor winding end turns against centrifugal force generated by rotor cyclic rotation. As the generator is operated, heated air accumulates within the end winding portions that are circumscribed by the retaining ring. Many known generator end winding cooling systems exhaust the heated air that would otherwise be confined within the retaining ring by either a forced axial flow path through the rotor body or a by a thermo pumping convective/centrifugal radial flow through channels formed in the rotor body teeth between successive rotor winding retaining channels.
In forced flow cooling systems cooling flow is generated by a pressure differential developed across the inlet and outlet of a cooling duct which forces air over the rotor end windings in a flow path that is generally axially oriented, parallel to the rotor shaft. Air channels are formed in the rotor body to exhaust air from within the retaining ring zone, which includes the rotor end winding portions, in an axially inboard direction to the rotor body. Once inboard the retaining ring, exhausted airflow is typically radially directed to the stator/rotor air gap by radially oriented portions of the rotor body air channels. Exemplary forced flow cooling systems are shown in U.S. Pat. Nos. 6,087,745 and 6,781,261.
Exemplary thermo pumping generator end winding cooling systems are shown in FIGS. 1 and 2 herein. It is believed that thermo pump-cooled systems offer advantages over forced flow cooling systems. Thermo pump-cooled systems do not require an externally applied pressure differential or auxiliary plenums and inlet guide baffles needed to route the cooling air to the end windings or to exhaust cooling air downstream of the end windings into channels formed in the rotor body. In thermo pump-cooled systems elongated serpentine ventilation paths do not have to be machined into the rotor body or end winding inter-coil insulation.
In thermo pump-cooled generator cooling systems relatively denser and cooler air in the retaining ring constrained region of the end windings is flung radially outwardly toward the end winding portions that are proximal the retaining ring. More specifically, FIGS. 1 and 2 show a known thermo pump-cooled generator 20, having a generator rotor 22, mounted on a rotor shaft 23. The rotor is circumscribed within a bore of stator 24, separated from each other by an annular air gap G. Electrical generator retaining rings 26 are coupled to the rotor 22 at each of the latter's axial ends. Rotor windings 28 have axial portions 29 that are respectively oriented within respective rotor winding channels 30, circumscribed by the stator 24 bore and the air gap G. The rotor winding channels are circumferentially separated by rotor teeth 32, into which are machined radial vent channels 34 and axial vent channels 36. The rotor teeth vent channels 34 and 36 are in communication with each other, so that heated air enters the axial vent channel 36 and is exhausted out of the radial vent channels 34 into the annular air gap G. Similarly other rotor air cooling axial vents (not shown) are formed in the rotor 22 radially inwardly below the rotor winding axial portion 29, which in turn vent radially into the annular gap G through vent holes 42 formed within wedge 40.
The rotor windings 28 also have end winding portions 44, including end turn bend portions, that extend outboard the annular air gap G. The end winding portions are circumscribed by the retaining ring 26. The retaining ring 26 supports the rotor winding end portions 44 end turns against centrifugal force generated by rotating rotor 22.